Here's an off-the-cuff version that uses regular expressions:

#!/usr/bin/perl

use strict; use warnings;

my $str = qq(just wondering how i can have perl display part of my lon
+g memo.  basically i want the first lets say 255 charachters of the p
+aragraph.  im really new to perl so i don't know how i would come abo
+ut this?);

my $max = 50;
(my $copy = $str) =~ s/(.{1,$max})\b.*/$1.../;
print "$copy\n";
__END__
[download]

What it does is match a maximum of $max characters and stores that in $1, a word boundary, then the rest of the string and essentially replaces the entire string with whatever it matched in $1 and an ellipsis. Matching the word boundary is nice so that you don't chop off the text in the middle of a word.

Update: Here's another way that does essentially the same thing:

my ($short) = $str =~ m/(.{1,$max}\b)/; $short .= '...';
[download]

This is probably how I would do it in my code, I just happened to think of the other way first for some reason.